A fragment of a charcoal drawing found in the Northern Territory has been carbon-dated by a New Zealand laboratory to 28,000 years ago, making it Australia's oldest known rock art specimen.

A specialist team led by Dr Fiona Petchey, based at the University of Waikato radiocarbon laboratory, pinpointed the age of the drawing, one of the earliest examples of human art on the planet. Previously, Australia's oldest known art was the "Bradshaw" figurative paintings found in the Kimberley region, dated to 16,000-17,000 years ago.

The fragment was discovered 60cm underground by Professor Bryce Barker, a University of Southern Queensland archaeologist originally from Kerikeri, who said it showed that - contrary to popular perception - Aborigines of that era were far from primitive.

When added to their use of stone tools and watercraft, "you're looking at some of the major first developments in modern human behaviour, and it's all happening here in Australia", he told the Herald.

Professor Barker found the granite fragment in June 2011 at a remote rock art shelter in Arnhem Land known as Narwala Gabarnmang, but it was only when he examined it in his laboratory four months later that he noticed the drawing. Because charcoal was used, Dr Petchey's team - who have just reported on their findings - was able to carbon-date it.

Narwala Gabarnmang, near the mouth of the Katherine River, has been called the "Sistine Chapel of rock art sites" - it is one of Australia's richest.

"When I first walked in, I was absolutely gobsmacked," said Professor Barker. "I had never seen anything like it."

An international team working at the site, at the request of the local Jawoyn people, has already found a 35,000-year-old edge-ground axe: a stone tool not developed elsewhere in the world until much later. The team, led by Melbourne's Monash University, includes Dr Petchey, who is internationally renowned in the radiocarbon-dating field.

The fragment may be part of a finely drawn "dynamic figure" - the oldest known rock art type in Arnhem Land. Cave paintings at Chauvet, in southern France, are estimated to be 34,000 years old, while drawings in the Spanish caves of El Castillo were dated only last week at about 40,000 years.